He was also facing two attempted murder charges related to passengers in the sedan, who were left with minor injuries, along with three counts of breaching apprehended violence orders.
Armstrong suffered serious brain and spinal injuries in the crash which resulted in the removal of part of his skull and the loss of use of his legs.
He was refused bail and has been in custody since June.
In a statement today, Corrective Services NSW said a 36-year-old man was found unresponsive in his cell at Metropolitan Remand and Reception Centre in Silverwater on Tuesday.
“The inmate was immediately given first aid and taken to hospital but was pronounced deceased,” a spokesperson said.
“As a matter of protocol, Corrective Services NSW and NSW Police investigate all deaths in custody regardless of the circumstances.”
Armstrong submitted a failed bail application last year, with the surviving passengers saying they were terrified of him.
He was due to face a committal hearing in July.
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